Eutectic Fatty Acids Phase Change Materials Improved with Expanded Graphite

Abstract

Low- and ultra-low-grade thermal energy have significant recycling value for energy saving and carbon footprint reduction. Efficient thermal energy storage technology based on phase change materials (PCMs) will help improve heat recovery. This study aimed to develop a composite eutectic fatty acid of lauric acid (LA) and stearic acid (SA) binary system with expanded graphite (EG). The experimental measured eutectic temperature was 31.2 °C with an LA-to-SA mass ratio of 7:3. Afterwards, 1~15 wt.% EG was composited to the eutectic acid, and the thermophysical properties of the composite PCMs were measured by differential scanning calorimetry (DSC) and transient plane source (TPS) methods. The results demonstrated that the phase transition temperature and latent heat of the composite PCMs were stable when the content of EG was more than 5%, and the thermal conductivity and thermal diffusion coefficient of the composite PCMs (10–15 wt.%) increased by 2.4–2.6 and 3.2–3.7 times compared with the pure eutectic acid, respectively. On this basis, a finned-coil-type reservoir was prepared, and an experimental study of heat storage and heat release performance was carried out. The results showed that the heat storage and heat release effects of the heat reservoir were the best when the EG ratio was 10 wt.%. The heat storage time was reduced by 20.4%, 8.1%, and 6.2% compared with the other three EG ratios, respectively; meanwhile, the heat release time was reduced by 19.3%, 6.7%, and 5.3%, respectively.

Expanded Graphite (EG) Stabilization of Stearic and Palmitic Acid Mixture for Thermal Management of Photovoltaic Cells

“…In the open literature, despite the existence of several works investigating the stabilization of PCMs within EG, the reported thermal conductivity values are generally low (from less than 1 W/(m K) [30,31] to 2.1 W/(m K) [32], rarely exceeding this value [29], along with the use of EG unless its fraction is higher than the PCM one [16]), and the PCM amount is limited to values below certain thresholds in order to avoid leaking (also below 70 wt.% [32]) with consequent complications in the production process and limitations in the use phase. In some works, thermal conductivity is enhanced only of less than 400% even with the addition of 20 wt.% EG [33].…”

Structural Analysis of Phase Change Materials (PCMs)/Expanded Graphite (EG) Composites and Their Thermal Behavior under Hot and Humid Conditions

“…Zanshe Wang et al. prepared fatty acid/EG composites and successfully increased thermal energy storage efficiency [28] . Ci Ao et al.…”

“…Zanshe Wang et al prepared fatty acid/EG composites and successfully increased thermal energy storage efficiency. [28] Ci Ao et al prepared SA/EG composites and revealed that more loading amount of EG in SA/EG composites supported higher thermal conductivity of SA/EG composites. [29] After optimizing PCM/EG composites with maximum PCM loading amount, PCM/EG composites are aimed for various applications.…”

Preparation and Thermal Performance of Fatty Acid Binary Eutectic Mixture/Expanded Graphite Composites as Form-Stable Phase Change Materials for Thermal Energy Storage

“…Energy storage technology is one of the effective methods to solve the energy crisis, and it has broad application prospects in the fields of shifting peaks and valleys of power, solar energy utilization, industrial waste heat recycling, building heating, and air conditioning. − Thermal energy storage can generally be divided into chemical energy storage, − sensible heat storage, and latent heat storage. , Latent heat storage has many advantages, including high energy storage density, low temperature change, excellent material stability, and high safety, so it has received a significant amount of attention and application. − Fatty acids have attracted much attention for their appropriate phase change temperature, high phase change latent heat, nontoxicity, noncorrosiveness, no or small volume change, small degree of subcooling, good thermal reliability, abundant raw materials, easily obtainable, and other advantages. , More importantly, two or more fatty acids can be mixed into a eutectic mixture according to the eutectic effect of fatty acids to reduce the phase change temperature and expand its temperature application range. , Although fatty acid eutectic mixtures have many advantages, they also have the disadvantages of poor thermal conductivity and easy leakage. − At present, the common method to solve these problems is to add materials with high thermal conductivity and porous structures to fatty acid PCMs. − Due to its low density, high thermal conductivity, and porous structure, expanded graphite (EG) is frequently utilized as a substrate material, which not only minimizes liquid leakage but also significantly improves the thermal conductivity of the PCMs. − …”